Paul rudolph



PLRUDOLPH. OBJECT GLASS (No Model) 1.1 llil lli,

Patented May 25,1897.

Fly]. X L a 9 n arrex,

UNITED STATES Seamhfimu PATENT OFFICE.

PAUL RUDOLPIL-OF JENA, GERMANY, ASSIGNOR TO THE FIRM OF CARL ZEISS, 0FSAME PLACE.

OBJECT-GLASS.

SPECIFICATION forming part of Letters Patent No. 583,336, dated May 25,1897. Application filed February 1, 1897- Sen'sl No. 621,475. No model.)

To all whom'it may concern.-

Be it known that I, PAUL RUDOLPH, doctor of philosophy, :1. subject ofthe Duke of Saxe- Altenburg, residing at Jena, in the Grand Duchy ofSaxe -lVeimar, German Empire, have invented a new and useful Ob'ect-Glass, of which the following is a specification,

The object of my invention is to provide a photographic objective which,while having a great intensity of light and over a wide field of viewbeing well. corrected as to astigmatism-that is to say, producing ananastigmatically-flattened imagemeets even exceptional requirements asregards chromatic and'spherical correction. This object is attained byrendering the principle of correction embodied in Gaussstelescope-objective serviceable for the purposes of the presentinvention.

Figure 1 represents the telescope-objective of Gauss. Fig. 2 representsan objective constructed according to the present invention.

Fig. 3 represents a doublet objective com-' l zosrid of twoobject-lenses of the improved Asis well known, Gauss has demonstratedthat a double-lens objective enables both chromatic and sphericalaberration to be corrected with great accuracy for a comparatively largeaperture if such compound object-lens be constructed as illustrated inthe section Fig. 1 of the accompanying drawings that is, if it consistsof a convex crown-glass meniscus A and a convexo-concave flint-glasslens B, the two surfaces whereof, which are turned toward each other andare separated by air, differing materially in their curva-- tures, sothat they may not be cemented together. Unlike the types ofobject-glasses of Fraunhofer, Littrow, and others, in which the facesturned toward each other have practically equal curvatures and aregenerally cemented together, the type of objective devised by Gauss isliable to. undergo on the basis of a proper distribution or arrangementof the curvatures a correction of the spherical aberration for twodifierent colors, so that the so-called chromatic difference of thespherical aberration is done away with and both aberrations are effacedover an area 001* responding to a large aperture. Objectives of thisdescription have been repeatedly and successfully applied toastronomical telescopes, both the arrangements of lenses that arepracticableviz., crown first and flint first-having been tried; butbefore the present invention no advantageous application of this type ofcompound. lens to photographic objectives has to my knowledge beeneither made or deemed feasible. Such application is attained in thefirst place by imparting to Gausss objective the property of producingan anastigmaticall flattened image, (which is so desirable forphotographic-lens systems, but which has hitherto not been realized inthe said objective,) and, secondly, by achro Y matizing suchanastigmatic objective in a novel manner satisfactory for photographicpurposes. In attempting to attain this result considerable diflicultyhas been experienced, owing to the narrow range of suitable sorts ofglass.

It has been found that in an objective of great aperture a perfectanastigmatic flattening of the image may be secured only withlenseseither of considerable thickness or placed at a great distanceapart. Furthermore, a suflicient chromatic correction, while asexpressed by the formula as it would have to comprise a very heavyflint-glass. According to the present invention this'drawback isobviated in the following manner. I

In the lens system shown in Fig. 1 either one lens, A, or the otherlens, 13, or both, consist each of a positive (biconvex) lens and of anegative (biconcave) lens cemented to the first and formed of-glas'shaving the same, or nearly the same, refractive power as the glass: ofthe positive component, but different dispersive power. A lens socomposed will, as regards all the effects dependent upon refrac- Itionevia, focal length, the location of the lens is equivalent to asingle lens with like curvatures and of a likethickness,but made ofglass having a d ispersivc power different from those which actuallyoccur in either part of the combiuatiom More specifically, the resultingdispersivepower of the compound lens is less than the least dispersivepower of the component lenscsthat is to say, the coinpoundlensisachromatic or partially achro matic-if the positive component (in casethe compound lens is a positive lens A) or the negativecomp'onent (incase the compound lens is a negative lens 1 consists of glass of lessdispersive'power, and the resulting dispersive power of the compoundlens is greater than that of either component-that is to say,

- the compound lens is hyperch'romatic-qf (in case the compound lens isa negative lens ll) the positive component is formed of glass of lessdispersive power than that of which the negative component is formed.The former fact agrees with the well-known rules of achromatiZation oflenses and the latter with the demonstrations respecting hypcrchromaticdispersing-lenses contained in mypending application for patent,- SerialNo. 598,201.

The, value of the resulting. dispersive power of the compound lens inall thcsecascs depends upon the values of the dispersive powercomponents and upon the ratio of the total curvatu res or of the focallengths of both components. It depends, consequently, if the outercurvatures of the compound lens are given, upon the radius of curvaturecommon to the inner surfaces united by cement. Such lenses A and B of alens system of the G'auss.

- is attended.

value may therefore be-calculated in each individual easeby means ofwell-known for mulae.

By the stated manncrof composing the typeevery required ratio of theirdispersive powers may be realized without causing the lenses to differfrom non-composite lenses of glass ofth'e samethicknessand outercurvatures as regards the effect of refraction andthe sphericalaberrations by which refraction "In order to correct sphericalaberration and to anastigmatically flatten the image, the outercurvatures and thicknesses of the lenses A and B consequently may bedetermined beforehand regardless of 'the' dispersive powers of theparticular kinds of glass to be employed, while the ratio of theresulting dispersing powers of the lenses A andB requisite for thepropercorrection of the chromatic aberrations can be readily establishedsubsequently by properlyxdetern'iining the inner radius of curvature ofthe components to be cemented of either or both lenses. In the ssaaaeratio result,.which in the case of non-composite' lenses could only beobtained by employing a flint-glass of a very high dispersive power, butwhich with lenses constructed as above explained are produced by crownand flint glasses, exhibiting but slightly diiferent dispersive powers,provided such glasses possessan equal orappmximately equal,- refractive'power. these requirementsin sufficient range of gradations form part ofthe kinds of optical glass which are constantly for sale at the JenaGlass W'orks. The condition 'of identical refractive power need only ofcourse be fulfilled approximately, inasmuch as slight differences in-theindiccs of refraction between the cemented components, even where thecurvature of the inner surface is very marked, influence the:corrections to only a Pairs of glasses which meet comparativelyinsignificant extent and may be easily introduced into the computations.Indeed, a little difference in the refractive powersay a few units inthe third place after the decimal point-may even prove advantageous,since, owing to such a difference,

-a more perfect equalization of the so-called zones of the sphericalaberration may become feasible. Apart from this no essential variationor departure from principle is 1nvolved in the construction ofobject-pieces of i the new types'hould some medium other than air beinterposed between the constituent parts of such object-piece, the oneimportant condition bein g that such separating or spac-f of the glassesemployed in, forming the two'- ing medium should possessan uncommonlysmall exponent index of refraction in comparison with theexp'onents ofthe'different kinds of glass employed.

it will be attended with the defect of ortho- 'sc'op'ic distortion ofthe image. .These two drawbacks may without difficulty be obviated,however, by constructing a double object glass with a central orintermediate dia pliragm, the objective hercinbefore described beingutilized as one of the constituent elements thereof. An example of thismodified form of the improved object-lens is givenin Fig. 3.

In the following examples, given by way of illustration of some forms ofthe new objec- "tive represented in Figs. 2'and 3,1 have introduced thefollowing symbols:

The letters r r r r r" designate the radii of the spherical ground-lenssurfaces.

d d (Z are the. central thicknesses of the lenses. 4 b'indicates thecentral-distance betweeu the diaphragm and the lens; 11, the central afront diaphragm, as shown in Figs. 2.

distance between the main parts of the lens system; L L U, the lensesthemselves, and D the diameter of the lenses.

In the following tables radii, thicknesses, and diameter of the lensesare expressed-in relative numbers, the focal length of the completeobjective being taken as a unit. By simply multiplying these numbers bythe focal length required in any given case the dimensions of an obectivc'possessing the requisite focal length will be found.

In order to characterize the difierent sorts of glass employed, therearegiven the refractive indices n and n relating, respectively, to the Dline of the solar spectrum and to the lly line of the hydrogen spectrum.for each kind of glass the value of the dis- A 2. persive power ismentioned, An being calculated for the interval between D and Hy, whilefor n the value it is adopted.

Example 1: Au astigmatically, spherically, and chromaticall y correctedobject-lens with The relative aperture of the objective is equal toone-ninth of the focal length. The objective consists of two componentsseparated from each other by air, the negative component being a singlelens L, while the positive part is made up of a dispersing-lens L and ofa collecting-lens If, both cemented together. The refractive indices ofboth sorts of glass employed in making the lenses L and L areapproximately equal, while the glass of which the lens L is formed isthe one possessing the higher dispersive power of the two.

Dimensions for a focal lcngthzl Maximum'relative aperturc:.1l1.

Thiclmesses and Alum" Dishmres.

,- 270s (repose Descripfions of Glass;

Besides,-

Dimensions for a focal length=1 Maximum relative apcrtnre=.25

T h'iclmesses and \Vhat I claim, and desire to secure by Let-- torsPatent of the United States, is

A compound objective which gives an anastigmatically-flattened image,consisting of two lenses (separated from each other by a medium oflittle refractive power), viz: one

- positive lens and one negative lens, at least one of which lenses ismade up of two constituent part-s united by cement and formed of twodiiferent sorts of glass of unequal dispersive power but nearly equalrefractive power, essentially as shown and described.

.In testimony whereof I have hereunto set my hand in the presence oftwo'subscribing witnesses.

.PAUL RUDOLPH.

lvitne ssesz 'RUnoLrH FRIcKE,

OTTO WOEDERLEIN.

